An attempt will be made to identify an ultraviolet absorbing compound developing from ampicillin by way of the penicilloic acid and to assess its role in allergic reactions to ampicillin. An attempt will be made to determine whether the ultraviolet absorption band developing in cephalothin solutions arises from a rearrangement analogous to the penicillenic acid rearrangement and what role this may play in hypersensitivity reactions. The bone marrow toxicity of 6-mercaptopurine in combination with allopurinol will be studied in rabbits. Effects of x-rays on intracellular pH and glycolytic mechanisms in Ehrlich tumor cells will be studied. Effects of a ketogenic diet on intracellular pH of mouse brain will be studied. Liver dihydropyrimidinase will be purified and its identity as the enzyme causing hydrolytic ring opening of 5-phenylhydantoin and Alpha- phenylsuccinimide investigated. Other drugs will be studied as possible substrates of this enzyme. Model compounds will be synthesized to ascertain what structural features are essential for susceptibility as a substrate.